1. Field of the Invention
The present invention relates to a laser processing apparatus having a parallelism adjusting function for bringing a laser beam oscillated by a laser oscillator into a parallel beam (collimated beam) in particular.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby partition a plurality of regions where devices such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the streets to thereby divide the regions where the devices are formed from each other, thus obtaining individual semiconductor chips. Further, an optical device wafer is provided by forming photodetectors such as photodiodes or light emitting devices such as laser diodes on the front side of a sapphire substrate. The optical device wafer is also cut along the streets to obtain individual optical devices divided from each other, such as photodiodes and laser diodes, which are widely used in electric equipment.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets, there has been put into practical use a method including the steps of applying a pulsed laser beam to the wafer along the streets to thereby form laser processed grooves on the wafer or modified layers inside the wafer along the streets and next breaking the wafer along the laser processed grooves or the modified layers. A laser processing apparatus for laser-processing a workpiece such as a wafer includes a chuck table for holding the workpiece and laser beam applying means for applying a laser beam to the workpiece held on the chuck table. The laser beam applying means includes a laser oscillator for oscillating a laser beam and focusing means for focusing the laser beam oscillated by the laser oscillator and applying the focused laser beam to the workpiece held on the chuck table (see Japanese Patent Laid-open No. 2006-51517, for example).
As described above, the laser processing apparatus for performing laser processing includes a chuck table for holding a workpiece and laser beam applying means for applying a laser beam to the workpiece held on the chuck table. The laser beam applying means includes a laser oscillator for oscillating a laser beam and a focusing lens for focusing the laser beam oscillated by the laser oscillator. In such laser beam applying means, the laser beam entering the focusing lens is preferably a parallel beam having a predetermined beam diameter. However, the laser beam oscillated by the laser oscillator has a divergence angle. Therefore, beam adjusting means for bringing the laser beam oscillated by the laser oscillator into a parallel beam is provided between the laser oscillator and the focusing lens.